Sale for specific items (gem store)
No. Sales are never announced, and if there is a certain rotation to the sales, the rotation cycle hasn’t been discovered yet (though I do not believe there is a rotation, but just the marketing team deciding what to put on sale).
Also, when it comes to armorskins, it also happens that specific skins are removed from the store. This to keep the list with skins not too long but still add refreshing new skins to it.
Arise, ye farmers of all nations
Arise, opressed of Tyria!
Arise, opressed of Tyria!